The present invention generally relates to a system and method for measuring and monitoring the elevation and shape of a silicon island during charge meltdown, granular silicon feeding in a crystal grower used to grow mono-crystalline silicon ingots.
The elevation and shape of the silicon island is critical to the quality of the silicon meltdown process which is in turn essential to the success of crystal growth from the silicon melt. The elevation and shape are affected by many variables in the meltdown process such as heater powers, granular poly feed rates, feeding locations, crucible positions, etc. To better ensure that the crystal growth is performed under optimal conditions, the silicon island should be measured and continuously monitored throughout the meltdown process. This can be difficult because the elevation of the silicon island is constantly changing and the shape of the island is also constantly changing and has very complex variations.
One existing method of measuring and monitoring a silicon island includes using a photo multiplier tube or charge-coupled device (CCD) cameras with a conventional light source (i.e., standard LEDs or the background radiation in the grower). This particular method, however, is not accurate enough to satisfy the control needs and is not capable of monitoring the silicon island in all meltdown conditions. Another method includes the use of a laser range finder or similar device. However, this method is not suitable for use in a crystal growth furnace because the laser beam generates reflection or scattering signals from the windows and heat shield on the furnace, causing significant errors in range finder measurements.
Thus, there exists a need for an effective means of continuously measuring and monitoring the silicon island during the meltdown process regardless of the conditions inside or outside of the crystal growth furnace. Furthermore, such means should not affect the meltdown or crystal growth process or pose harm to the operators.